There are two main rationales for implementing balance and fade behavior in a multi-loudspeaker audio system. The first is to re-position the audio image within the listening space to accommodate particular user preferences. The second is to re-locate the audio to avoid disturbing listeners within certain regions of the listening space. Existing audio system implementations address either one or the other of these divergent goals but not both, leading to a non-ideal solution in each case.
Re-positioning the audio implies that the user wants to tailor the acoustic sound field to an individual preference, but still desires overall sound quality for all listeners. In this case it is essential that multiple loudspeakers remain active (albeit with different gains) so that an even timbre and proper acoustic summation is maintained throughout the listening environment. For example, if the user chooses to fade the audio to the front, it is desirable that the rear speakers continue to play at least a portion of their low-frequency content to avoid producing unintended acoustic dips within the space.
In contrast, re-locating the audio implies that the user wants to isolate or focus the audio to certain areas of the listening environment to not disturb certain listeners. In this case, the user is willing to sacrifice some total sound quality to achieve this goal. Therefore, the loudspeakers located near the undesirable listening zones may be completely muted to reduce the acoustic output experienced by those listeners to the extent possible. In some cases it is also desirable to filter the audio to remove low-frequency content due to the nature of its omni-directional propagation. This muting and filtering provides for a non-ideal listening experience to those listeners in the active zone.
In various types of audio systems, the user can adjust the left/right balance and front/rear fade from a default or detent setting within a certain range. The detent positions may be designed to provide for optimum audio output across the main listening area of an intended listening environment. Progressively changing the balance control or input progressively moves the audio output to the left or right of the listening environment by adjusting the signal processing of one or more loudspeakers relative to one another. Fade control operates in a similar fashion to progressively move the audio output toward the front or rear of the listening environment.
A simple prior-art implementation achieves this by progressively adjusting the gain on the loudspeakers in response to each adjustment of the control away from the detent or default position. When a control is at the end of its range, the affected loudspeakers will be muted. However, this may result in compromising sound quality as perceived by users in one or more listening zones. This may be particularly noticeable in applications where multiple loudspeakers may be arranged around the listening environment, and may have different frequency responses such as those associated with a woofer, mid-range, or tweeter, for example, to provide a desired spatial sound image or distribution.
One solution that maintains audio quality across the range of balance/fade settings is to modify the output of the loudspeakers by simultaneously adjusting gain, filtering, and/or other signal processing parameters in tandem with the balance and fade controls. For these applications, all of the loudspeakers may still be producing some acoustic output even when a balance and/or fade control is adjusted to a maximum or minimum setting at the end of its range. However, this effect may be inconsistent with listener expectations and result in complaints or warranty claims. For example, listeners may expect certain speakers to have zero perceptible audio output based on balance and/or fade being adjusted to their maximum or minimum positions.